1. Field of the Invention
The present invention relates generally to a head rest device for an automotive vehicle wherein a head rest proper is pivotally supported on a seatback by means of a frame. More specifically the present invention relates to an improved arrangement for affixing the headrest to the frame.
2. Description of the Prior Art
An illustrative example of a conventional head rest device for employment in an automobile is the device which is disclosed in Japanese Patent Second Provisional Publication No. 57-45.
In the disclosed head rest device, two grooves each of which are triangular in cross section, are formed in opposing sections of the metal interior structure of the head rest. These grooves define a clamping support channel, generally square in cross section, in which a central section of the support stay by which the head rest is affixed to the seat is accommodated.
The support stay is gripped in the support channel which applies a given amount of surface pressure thereto for providing a desired degree of frictional resistance to relative pivotal movement of the headrest device about the axis defined by the generally horizontal central section of the support stay.
When adjustment of the inclination angle of the headrest proper becomes necessary or desirable, the headrest proper is pivotally moved against the frictional resistance provided by the engagement between the clamping support channel and the support stay.
When constructing a headrest according to the above described prior art, generally the support stay is inserted into one of the channels defined by two panels which form the semi-rigid internal structure of the head rest and thereafter the other of the two panels is welded to the first panel such that the o stay is permanently pressed between the two panels with what is hoped to be the engaging pressure that will provide the optimum degree of frictional resistance to rotation of the headrest.
In the above type of head rest, some disadvantages are encountered. One of the disadvantages of the above described prior art head rest device has to do with the difficulty, that is inherent to a structure of this sort, which one encounters when trying to provide the optimum degree of frictional resistance to relative rotation, which is to be obtained through the engagement between the channel and the central horizontal section of the stay.
This frictional resistance is provided by the resilience of the grooves defining the clamping support channel, whose shapes must be resiliently altered in order to accommodate the stay within the clamping support channel which they cooperate to define. The degree to which the dimensions of the grooves are altered determines the degree of frictional resistance which the orifices exert on the stays. Therefore, in order to consistently produce the desired degree of frictional resistance to rotation of the head rest in the prior art device, it is necessary to manufacture the clamping sections of the head rests to very strict tolerances.
This attention to the precision with which the clamping sections of the head rest units must be formed tends to add substantially to the cost of their production.
In a proposed alternative arrangement to the above-mentioned prior art head rest, the semi-rigid internal structure of a head rest device is affixed to the central horizontal section of the support stay by means of a pressure clamp which is arranged on the outer surface of the rigid internal structure. In such an arrangement, a metal clip having tabs with registered holes is placed on the central section of the stay. A bolt is passed through the registered holes in the tabs, through a hole in the bottom surface of the semi-rigid internal support member of the head rest and has a nut threaded onto an end thereof.
When the bolt is rotated with respect to the nut, in the tightening direction, the lowermost tab is urged toward the upper tab which is in engagement with the lower surface of the semi-rigid internal structure of the head rest and therefore is restricted from moving upward. As the gap between the two tabs is closed by means of the bolt, the clip is caused to tighten onto the central section of the support stay. Since the bolt passes through the hole formed in the semi-rigid support structure of the head rest, this tightening of the bolt also serves to affix the clip to the lower surface of the semi-rigid structure of the head rest. Thus, the clip or pressure clamp may be bolted onto the lower surface of the semi-rigid internal structure.
As will be appreciated from the above the stay is attached at its central section to the semi-rigid internal support structure of the head rest by means of the bolt by which the clamping pressure of the clip is applied.
In such an alternative head rest, it will be noted that the precision with which the elements forming the semi-rigid internal structure of the head rest are formed can be somewhat reduced relative to that required in the previously described prior art bead rest in which the two halves forming the semi rigid internal structure of the head rest are permanently welded together. This is because the frictional resistance of the head rest to rotation about the central horizontal section of the support stay can be adjusted by adjusting the tightness of the bolt by which the head rest is affixed to the stay.
Thus, in this head rest, it is possible to select a value of frictional resistance to rotation of the head rest about the axis of the central section of the support stay which allows the user to adjust the angle of the head rest relative to the seat back such that the head rest is in the position which provides the maximum comfort to the user.
There is a problem however in the above proposed head rest, in connection with the fact that the head rest is affixed at its lower surface to the stay. Adjustment of the head rest causes it to pivot about the axis of the central section of the support stay. Since the support stay is arranged at the bottom of the head rest, it is impossible to adjust the angle of the head rest without causing main portion of the head rest to come forward of the general plane of the seat back to an uncomfortable degree, or to pivot backwards to a point where the head rest no longer supports the head of the vehicular seat's occupant.
As is well known to those skilled in the art, it is the purpose of the head rest to help to prevent injury to the head and neck of the vehicular seat occupant by preventing the occupant's head from swinging suddenly and violently backwards relative to the occupants body, resulting in the type of injury known as whiplash. In view of this, another problem exists in that, if the resistance to frictional rotation of the latter described head rest is adjusted, by means of the bolt, to a value which allows reasonably easy angular adjustment of the head rest by the user, in the event of vehicular traffic accident, such as a rear end collision, the forces applied by the occupant's head to the head rest easily cause it to pivot backward and thus it becomes practically useless as far as the enhancement of the vehicular seat occupant's safety is concerned. What is more, when the head rest pivots backwards under the impact of the occupant's head, the head or the shaft, of the bolt by which the head rest is fastened to the stay is caused to face in the direction of the back of the occupant's head and could perforate the occupants skin and, if the force of the impact is great, may crack the occupant's skull or spine.
The same concern would hold true for the occupant of the rear seat of the vehicle whose head would come into violent contact with the rear side of the head rest in the event of a head on collision causing it to pivot forward and expose the bolt on the bottom thereof to the rear seat occupant's face.
The problems of the head rest pivoting backwardly under impact of the occupant's head may be overcome in a variant on the above arrangement in which the clip, by which the seat back head rest is attached to the horizontal middle section of the support stay, is positioned on an inner surface of the semi-rigid internal structure of the head rest.
In this manner, the head rest supporting clip can be arranged at a point in the head rest that is rear the vertical center thereof. Therefore when the head of the occupant comes into contact with the head rest under the pressure of impact the direction of the pressure is essentially on the pivoting axis of the head rest on the stay and therefore the head rest is under no particularly strong impetus to rotate about the support stay.
Unfortunately in the latter arrangement of the head rest, the safety of the head rest is not particularly improved. This is due in part to the fact that normally, in order to cushion the blow to the seat occupant's head in the event of a rear end accident, it is desirable that the inner structure of the head rest is somewhat resilient so that the inner structure absorbs some of the impact which would otherwise be transmitted from the vehicle body to the seat back and from the seat back to the seat occupant's head by means of the support stay and the head rest. In the latter proposed head rest above however, the clip by which the head rest is attached to the stay is provided at the central section of the head rest and therefore the support stay is essentially aligned with the back of the occupants head. Thus, the resilience of the internal structure of the head rest cannot be advantageously used to protect the occupant's head from contact with the horizontal section of the support stay. Therefore, the only effective cushioning resilience that can be provided is that provided by the layer of resiliently cushioning material on the front surface of the head rest. This cushioning material must, of course, be somewhat soft and resilient so that when the occupants head impacts the head rest, the layer of cushioning material becomes resiliently compressed so as to cushion the occupants head from violent contact with the rigid support structure of the head rest.
Unfortunately in the above arrangement, if the cushioning material is appropriately soft to adequately cushion the occupant's head in the event of a rear impact to the vehicle, then when it is compressed during impact with the occupants head the problem is again encountered that the occupant's head comes into forcible contact with either the support stay or the head or the shaft of the bolt by which the head rest is attached, via the clip, to the support stay, since the bolt and the stay are buried in the padding material at the front side of the head rest. This again places the seat occupant in danger cf injury due to forcible contact with the head of the bolt by which the head rest is attached to the stay.